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The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages, and a few new episodes were posted. Now, the blog/podcast is on a weekly schedule with diverse topics, and the Facebook Page showcases photos on Mineral Monday and Fossil Friday. Thanks for your interest!

Tuesday, December 2, 2014

December 2. Cenozoic Time

The Tertiary and Quaternary, the original periods of the Cenozoic, were divided into epochs by Charles Lyell in 1833, and the names he gave are still retained, although they are now assigned to the Paleogene, Neogene, and Quaternary Periods.

He used the same root word, “cene,” meaning recent, that is the prefix of the era, Cenozoic, but Lyell used it as a suffix when he named the epochs. He had analyzed assemblages of fossils from the different Cenozoic formations, and using the percentages of species that still were alive at present, he assigned names to the time periods that were marked by increasingly modern or recent fossil assemblages. He named the Eocene, which means “dawn-recent,” for rocks with fewer than 5% of modern species present, Miocene, “less recent,” for those that had 20-40% of modern species, and Pliocene, “more recent,” for those that were 40% to 90% modern. Since Lyell’s time, we’ve added Paleocene, “ancient-recent,” with essentially no modern species, Oligocene, “little or few-recent,” Pleistocene, “most recent,” and Holocene, “entirely recent.”

In order from oldest to youngest, the epochs are Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. There’s been a lot of discussion about naming a new epoch, the Anthropocene, which means “human-recent,” for the last few thousand years, but the Holocene is only about the past 12,000 years so there would be considerable overlap. In my opinion it’s all semantics and preference and doesn’t matter.

The Paleocene, which began with the end of the Cretaceous, and the Eocene and Oligocene make up the Paleogene Period. The Miocene and Pliocene are the Neogene Period, and the Pleistocene and Holocene are the epochs of the Quaternary Period. The boundary between the Paleogene and Neogene is put at 23 million years ago, and the Quaternary started 2.5 million years ago and basically coincides with the glacial age.

So, that makes the Paleogene about 43 million years long, pretty typical for a geological period, and the Neogene is 21 million years long, which is on the short side. The Quaternary, at 2.5 million years, is an exceedingly short time span for a period, but it’s OK because we know so much about it, and because it does represent a time when things changed a lot, the modern ice ages. There is some argument as to whether the Quaternary should be seen as a full-fledged period or should be an epoch of the Neogene. All semantics and technicalities. For now I’m going with what I perceive to be the internationally recognized scheme that has the Quaternary as a period, not that it really matters.

I realize that that’s a lot of jargon and detail. I’ll try over the course of the month when I use names like Oligocene or whatever to keep it clear where we are as we progress through the Cenozoic.

Bret Harte

Let me close with a poem by Bret Harte, author and poet of the California Gold Rush. His poem, To the Pliocene Skull, was written in response to reports in the daily press of 1868: "A human skull has been found in California, in the pliocene formation. This skull is the remnant not only of the earliest pioneer of this State, but the oldest known human being. The skull was found in a shaft 150 feet deep, two miles from Angels in Calaveras County, by a miner named James Watson, who gave it to Mr. Scribner, a merchant, who gave it to Dr. Jones, who sent it to the State Geological Survey. . . . The published volume of the State Survey of the Geology of California states that man existed here contemporaneously with the mastodon, but this fossil proves that he was here before the mastodon was known to exist.” Harte was clearly skeptical of this discovery, and rightfully so.

The intro music is from "Vintage Education" by Kevin MacLeod; public domain from freepd.com. Banner photos by Richard Gibson unless credit line is given. Then, they are either public domain or are used with permission of the photographer.